Printing and developing photographs on silver-chlorid paper.



UNITED STATES PATENT OFFICE.

HERBERT JOHN MALLABAR, QF LIVERPOOL, ENGLAND, ASSIGNOR TO SYNOLOIDS LIMITED, OF LONDON, ENGLAND.

PWG AND DEVELOPING rHOTOGRAPHB ON SILVER'CHLORID PAPER.

Specification of Letters Patent.

was. April 13, 1909.

application filed July 8, 1905. 861181 No. 288,688.

To all whom it may concern:

am, and residing in Liverpoo in the county of Lancaster, in the Kingdom of Englan photographic chemist, have invented certain new and useful Improvements in Printing and Developing Photographs on Silver-Chlorid Paper.

This invention has for its object a new or improved fill'ocess for printing and developingsilver c orid paper whereby much greater speed of operation is obtained, the cost is ve much lower than in the gold process, an the results are more brilliant and show The invention consists mainly in using c anids or sulfocyam'ds in the developer. l practice I propose to form the chemicals into tablets; one tablet to contain 4 grains of pyro allic acid with or without inactive mate ri and the other to contain one-thirtieth of a grain of bichromate of potash, one-fourth greater detail.

of a grain of sulfocyanid of potassium (KCN S) and one grain of citric acid with or without inactive material such as su er of milk the fimction of this material being to increase the bulk'. These two pellets or tablets are dissolved in about five ounces of water. I do not however bind myself to these exact details. Taking the various chemicals separately, in place of pyrogallic acid I may use about the same weight of metol. If metol be used it gives a blacker tone, and increases the speed of development. One and a half grains of metol and three grains of hydroquinone give a tone midway between pure metol and pure pyrogallic acid. There are other reducin agents similar to these which can be use; in substitution of them, but not with such good effect. The bichromate of potash is used to increase the speed of development, and other alkaline bichromates can replace the bichromate of potash, but there is no advantage in using any of these over the potash salt, which is at the same time the cheapest, the most easily obtainable, the purest and the most satisfacto for my u ose. In place of anhydrous su focyani o potassium, an alkaline iodid, sulfocyanid of sodium or even of ammonium could be"used, but the ammonia salt discolors quicker and it cannot be made in the tablet form. Alkaline cyanids can also be used to a certain extent, but from my experiments I find that none of these salts are equal in value to the anhydrous sulfocyanid of potassium, and further sulfocyanid of potassium is non-poisonous whereas cyanide are ve poisonous. I say anhydrous, as althou the hydrated salt will work equally well, t e

anhydrous salt can be made into tablets, and

is not so deliquescent, whereas the hydrated salts are very deliquescent, and therefore it is diflicult to keep them in pellets of exact weight and quantity. The uantity of sulfQ- cyanid too can be considera ly varied, thus where a considerable amount extra is added, and the printing is carried dee er in the first instance, I obtain a fine Barto ozzi red tone. The citric acid I use is specially pure and free from sulfuric acid and lime and is deprived of its water of crystallization, one grain of it egg als 1.120 grains of ordinary citric acid orysta It is used to make the (level? 0 er work more evenly and to remove the hi- 0 romate stain. It can also be substituted in whole orin part by tartaric and other vegetable acids of a like nature, but from m experiments I have found that citric acid is decidedly the best.

I will now give an illustration of the carrying out of my invention. Sensitized paper is placed behind the negative in the usual man ner, and exposed to actinic light. When it is printed to about one-third of the depth necessary for the usual method of gold toning, it is placed at once into the developing bath without previous was this developing bath being composed oi about five ounces of water to each lpair of tablets. When sufficiently developed t e print is laced in a fixing solution of hyposulfite of so a, say two ounces to one pint of water. When in this fixing bath, the print turns first to a ellowish color, but when the fixing is comp ete say in from ten to fifteen minutes, it Is found that the print has arrived at the requisite color. It is then washed as usual and dried. This process I have found by experiment will develop about one hundred cabinet prints for one penny of chemicals, according to the prices now ruling in Great Britain, and each rint only takes about a minute and a half to evelo while the result is superior to anything can obtain from any other process. As far as my experiments have gone to, these prints are more permanent than the ordinary gold toned prints.

I have found in practice that iodid of potassium, and in fact other alkaline iodids will work substantially as well as the sulfocyanids, and I wish it to be understood that s I wish to claim these also as the equivalent of the sulfo-cyanids.

I declare that what I claim is:

1. The process of printing and developing silver chlorid paper, which consists in printing to about one-third the depth required by the ordinary gold process, immersing the paper in a mixture 0 a reducing agent, such as described, a bichromate, sulfocyanid of potassium, citric acid and water, and then fixing, substantially as described.

2. The step in the process of printing and developing ordinary sensitive paper, which consists in immersing the exposed paper in a mixture of a reducing agent, such as described, with a bichromate, anh drous sulfocyanid of potassium, citric aci and water, substantia 1y as and in the proportions described.

3. The process of printing and developing silver chlorid paper, which consists in first printing, then immersing the print in a reducing agent containing a sulfo-cyanid, and then fixing.

4. The process of printing and developing ordinary sensitized paper which consists in forming two sets of tablets as follows; tablet A, 240 parts by weight of a reducing agent,

as described, and tablet B, two parts by weight of a mineral alkali bi-chromate, sixty parts by wei ht of citric acid, and 15 parts y weight 0 making a bath of an equal number of tablets of each of these. sets with the requisite amount of water to form the developer, and develo ing therein.

5. e process of developing photogra hic images in silver sensitive pa ers by ad g an alkaline sulfo-cyanid to t e developer.

6. The process of developing photographic images in silver sensitive pa ers, which consists in adding to the devel d er a chemical that shall instantly seize on t e nascent silver and convert it to an insoluble, non-adhesive, crystalline salt.

7. The process of printing and developing ordinary silver sensitized paper, which consists in first printing, then immersing the print in an acidreducing agent, containing one of the well known re-agents which preci itates silver in an acid so ution'in theform 0 a crystalline, non-adhesive salt.

In witness whereof, I have hereunto signed my name in the presence of two subscribing witnesses.

HERBERT JOHN MALLABAR. Vvitnessesa- WILLIAM P. THOMPSON, 'WILLIAM HENRY BEESTON.

a sulfocyanid of potassium, 3 

